A wireless communication device in a communication system communicates directly or indirectly with other wireless communication devices. For direct point-to-point communications, the wireless communication devices participating in the communication system tune their receivers and transmitters to the same channel(s) and communicate over those channels. For indirect wireless communications, each wireless communication device communicates directly with an associated base station and/or access point via an assigned channel.
Each wireless communication device participating in wireless communications includes a built-in radio transceiver (i.e., transmitter and receiver) or is coupled to an associated radio transceiver. Typically, the transmitter includes one antenna for transmitting radiofrequency (RF) signals, which are received by one or more antennas of the receiver. When the receiver includes two or more antennas, the receiver selects one of antennas to receive the incoming RF signals. This type of wireless communication between a transmitter with one antenna and receiver with one antenna is known as a single-output-single-input (SISO) communication.
Well known communications systems provide a range extension on a SISO system by reducing the data rate and, as a result, increase the symbol duration and/or increasing transmit power. However, increasing transmit power can lead to increase interference to other users sharing the network. The preferred method for improved range reception does not lead to decreased network capacity. For popular multicarrier systems such as SISO WLANs, range improvement is achieved by taking an 802.11a/802.11g signal and cutting the symbol rate. Specifically, the 802.11ah is the range extension an amendment of the IEEE 802.11-2007 wireless networking standard. The goal of the amendment is to optimize the rate vs range performance of the specific channelization. One proposed method to achieve range extension is by down sampling the 802.11a/802.11g physical layer into 26 channels. When the symbol clock is divided by 26, each symbol duration becomes 104 μsec and the corresponding rate for each subcarrier becomes 12 kbps. Keeping the other system parameters, the same, (e.g. number of data carriers, cyclic prefix percentage, etc.), the bandwidth for a signal is reduced as well the integrated thermal noise power at the receiver. Therefore, for the same transmit power as 802.11a/802.11g, the thermal noise floor is decreased by 10*log 10 (26). This results in a 14 dB “gain” in the sensitivity of the receiver which is equivalent to at least 5 times improvement in the range of an over existing WLAN. What is needed is a communication device, system and method that increases the transmission range of existing WLAN for specific applications without impacting the data rate and which adds flexibility to address new markets for high connectivity environments. A suitable invention would improve transmission characteristics of targeted devices without an increase in interference of other nearby wireless systems and devices. Therefore, what is needed is a method for improved range reception that does not lead to decreased network capacity or increased susceptibility to interference of the wireless device.
Generally speaking, transmission systems compliant with the IEEE 802.11a and 802.11g or “802.11a/g” as well as the 802.11n standards achieve their high data transmission rates using Orthogonal Frequency Division Modulation (OFDM) encoded symbols mapped up to a 64 quadrature amplitude modulation (QAM) multi-carrier constellation. In a general sense, the use of OFDM divides the overall system bandwidth into a number of frequency sub-bands or channels, with each frequency sub-band being associated with a respective sub-carrier upon which data may be modulated. Thus, each frequency sub-band of the OFDM system may be viewed as an independent transmission channel within which to send data, thereby increasing the overall throughput or transmission rate of the communication system. Similarly, multi-code spread spectrum system comprised of perfectly orthogonal high-speed chaos spreading codes transporting independent modulated data can be used to increase its overall throughput or transmission rate of the SISO system. The high-speed “spreading signals” belong to the class of signals referred to as Pseudo Noise (PN) or pseudo-random signal. This class of signals possesses good autocorrelation and cross-correlation properties such that different PN sequences are nearly orthogonal to one other. The autocorrelation and cross-correlation properties of these PN sequences allow the original information bearing signal to be spread at the transmitter.
Transmitters used in the wireless communication systems that are compliant with the aforementioned 802.11a/802.11g/802.11n standards as well as other standards such as the 802.16a IEEE Standard, typically perform multi-carrier OFDM symbol encoding (which may include error correction encoding and interleaving), convert the encoded symbols into the time domain using Inverse Fast Fourier Transform (IFFT) techniques, and perform digital to analog conversion and conventional radio frequency (RF) upconversion on the signals. These transmitters then transmit the modulated and upconverted signals after appropriate power amplification to one or more receivers, resulting in a relatively high-speed time domain signal with a high peak-to-average ratio (PAPR).
Transmitters used in direct sequence spread spectrum (DSSS) wireless communication systems such as those compliant with commercial telecommunication standards WCDMA and CDMA 2000 perform high-speed spreading of data bits after error correction, interleaving and prior to symbol mapping. Thereafter, the digital signal is converted to analog form and frequency translated using conventional RF upconversion methods. The combined signals for all DSSS signals are appropriately power amplified and transmitted to one or more receivers.
Likewise, the receivers used in the wireless communication systems that are compliant with the aforementioned 802.11a/802.11g/802.11n and 802.16a IEEE standards typically include an RF receiving unit that performs RF downconversion and filtering of the received signals (which may be performed in one or more stages), and a baseband processor unit that processes the OFDM encoded symbols bearing the data of interest. The digital form of each OFDM symbol presented in the frequency domain is recovered after baseband downconverting, conventional analog to digital conversion and Fast Fourier Transformation of the received time domain signal. Whereas receivers used for reception for DSSS must de-spread the high signal after baseband downconverting to restore the original information signal band but yields a processing gain equal to the ratio the high speed signal to information bearing signal. Thereafter, the baseband processor performs demodulation and frequency domain equalization (FEQ) to recover the transmitted symbols, and these symbols are then processed with an appropriate FEC decoder, e.g. a Viterbi decoder, to estimate or determine the most likely identity of the transmitted symbol. The recovered and recognized stream of symbols is then decoded, which may include deinterleaving and error correction using any of a number of known error correction techniques, to produce a set of recovered signals corresponding to the original signals transmitted by the transmitter.
To further increase the number of signals which may be propagated in the communication system and/or to compensate for deleterious effects associated with the various propagation paths, and to thereby improve transmission performance, it is known to use multiple transmission and receive antennas within a wireless transmission system. Such a system is commonly referred to as a multiple-input, multiple-output (MIMO) wireless transmission system and is specifically provided for within the 802.11n IEEE Standard and 3GPP LTE Advanced standard. As is known, the use of MIMO technology produces significant increases in spectral efficiency, throughput and link reliability, and these benefits generally increase as the number of transmission and receive antennas within the MIMO system increases.
In particular, in addition to the frequency channels created when using OFDM, a MIMO channel formed by the various transmit and receive antennas between a particular transmitter and a particular receiver includes a number of independent spatial channels. As is known, a wireless MIMO communication system can provide improved performance (e.g., increased transmission capacity) by utilizing the additional dimensionalities created by these spatial channels for the transmission of additional data. Of course, the spatial channels of a wideband MIMO system may experience different channel conditions (e.g., different fading and multi-path effects) across the overall system bandwidth and may therefore achieve different signal-to-noise ratio (SNRs) at different frequencies (i.e., at the different OFDM frequency sub-bands) of the overall system bandwidth. Consequently, the number of information bits per modulation symbol (i.e., the data rate) that may be transmitted using the different frequency sub-bands of each spatial channel for a particular level of performance may differ from frequency sub-band to frequency sub-band. Whereas DSSS signal occupies the entire channel band, the number of information bits per modulation symbol (i.e., the data rate) that may be transmitted using the different DSSS sequence for each spatial channel for a particular level of performance.
In the MIMO-OFDM communication system using a typical scheme, a high Peak-to-Average Power Ratio (PAPR) may be caused by the multiple carrier modulation. That is, because data are transmitted using multiple carriers in the MIMO-OFDM scheme, the final OFDM signals have amplitude obtained by summing up amplitudes of each carrier. The high PAPR results when the carrier signal phases are added constructively (zero phase difference) or destructively (±180 phase difference). Notably, OFDM signals have a higher peak-to-average ratio (PAPR) often called a peak-to-average power ratio (PAPR) than single-carrier signals do. The reason is that in the time domain, a multicarrier signal is the sum of many narrowband signals. At some time instances, this sum is large and at other times is small, which means that the peak value of the signal is substantially larger than the average value. Similarly, MIMO-DSSS schemes can have high PAPR for periodic sequence or binary-valued sequence; however, chaos spreading sequences do not exhibit either of these characteristics and therefore have better PAPR performance for SISO and MIMO operations.
Common PAPR reduction strategies include amplitude clipping and filtering, coding, tone reservation, tone injection, active constellation extension, and multiple signal representation techniques such as partial transmit sequence (PTS), selective mapping (SLM), and interleaving. These techniques can achieve significant PAPR reduction, but at the expense of transmit signal power increase, bit error rate (BER) increase, data rate loss, increase in computational complexity, and so on. Further, many of these techniques require the transmission of additional side-information (about the signal transformation) together with the signal itself, in order that the received signal to be properly decoded. Such side-information reduces the generality of the technique, particularly for a technology where one would like simple mobile receivers to receive signals from a variety of base station transmitters. Alternatively, properly designed chaos spreading sequences can be utilized as a phase dithering sequence added to MIMO-OFDM and OFDM composite carrier signal to reduce PAPR and send side-information about the signal transformation without substantially increasing transmit signal power or degrading the BER at the receiver.
In many geographic regions, there is a desire for heterogeneous networks such as MIMO-OFDM system and Digital Chaos Cooperative Network, to share a common band of frequency to alleviate the “spectrum crunch” being experienced by the overwhelming demand for data in a finite radio frequency spectrum. One such approach to handle this coordination or sharing is dynamic spectrum access (DSA). DSA networks evaluate different degrees of interaction between primary users and secondary users to control out-of-bound interference (i.e., “emissions”) between the primary user's transmissions and the secondary user's transmissions. In DSA networks including underlay transmission, secondary users may communicate with each other as long as the interference measured between the primary user transmission and the secondary user transmission is below some predefined threshold. In this case, the secondary users not only assess whether primary users are transmitting but also how much interference or emissions the secondary user transmission will create and whether the secondary user's transmission will disrupt the primary user's transmission. On the other hand, in DSA networks having overlay transmissions, the primary user and the secondary user are permitted to communicate in a cooperative fashion. Lastly, in any DSA network including both underlay transmission and the overlay transmissions, or in DSA networks having a combination of overlay and underlay networking, it is necessary to evaluate the impact of the presence of secondary user's transmission on primary user transmissions to determine the overall efficient of the transmission.
In spectrum and regulatory body communities, DSA has broad connotations and encompasses various approaches to spectrum reform. One such approach is the category of Hierarchical Access Model, based on comparative evaluation of primary user transmissions and secondary user transmissions. Evaluating the transmissions includes controlling the primary and secondary user operations. Typical examples of evaluating secondary user operations involve controlling out-of-bounds emissions or interference based on the composite PAPR of a transmitting station engaged in concurrent primary user and secondary user operations. In this instance, “concurrent” may mean that the primary user stream and the secondary stream are transmitting simultaneously out of the same antenna structure. The “composite PAPR” is calculated using signals from each primary user transmission and secondary user transmission and calculating a total PAPR for a collection of primary and secondary users transmission. Secondary user operations include secondary user transmissions in a dynamic spectrum access network (DSA). Overlay signal transmissions and underlay signal transmissions are examples of secondary user transmissions found in DSA networks, which can be controlled based on evaluation of the composite PAPR and one other constraint according to this invention.
The continually increasing reliance on SISO and especially MISO wireless forms of communication creates reliability and privacy problems. Data should be reliably transmitted from a transmitter to a receiver. In particular, the communication should be resistant to noise, interference, and possibly to interception by unintended parties.
In the last few years there has been a rapidly growing interest in ultra-wide bandwidth (UWB) impulse radio (IR) communication systems. These systems make use of ultra-short duration pulses that yield ultra-wide bandwidth signals characterized by extremely low power spectral densities. UWB-IR systems are particularly promising for short-range wireless communications as they combine reduced complexity with low power consumption, low probability of detection (LPD), immunity to multipath fading, and multi-user capabilities. Current UWB-IR communication systems employ pseudo-random noise (PN) coding for channelization purposes and pulse-position modulation (PPM) for encoding the binary information.
Others have proposed a periodic sequences of pulses in the context of chaos-based communication system. Additional work has relied upon the self-synchronizing properties of two chaotic systems. In such a system, data is modulated into pulse trains using variable time delays and is decodable by a coherent receiver having a chaotic generator matched to the generator used in the transmitter. Such system is known in the art as a Chaotic Pulse Position Modulation (CPPM) scheme.
Chaotic dynamical systems have been proposed to address the problem of communication privacy. Chaotic signals exhibit a broad continuous spectrum and have been studied in connection with spread-spectrum applications. The irregular nature of a chaotic signal makes it difficult to intercept and decode. Therefore, receivers that do not have knowledge of the chaotic signal will not be able to distinguish the chaotic signal from noise or interference. In the context of UWB systems the use of non-periodic (chaotic) codes enhances the spread-spectrum characteristics of the system by removing the spectral features of the signal transmitted. This results in a lower probability of interception/detection (LPI/LPD) and possibly less interference towards other users. This makes the chaos-based communication systems attractive.
There remains a need for improved chaotic coding/modulation methods to produce such attractive communication systems. One prior art, U.S. Pat. No. 6,882,689, issued Apr. 15, 2005 to Maggio et al., attempts to improve chaotic coding using pseudo-chaotic coding/modulation method that exploits the symbolic dynamics of a chaotic map at the transmitter to encode data. The method uses symbolic dynamics as “coarse-grained” description of the evolution of a dynamic system. The state space is partitioned and a symbol is associated with each partition. The Maggio invention uses a trajectory of the dynamic system and analyzes it as a symbolic system. A preferred transmitter of the Maggio prior art accepts digital data for coding and the digital data is allocated to symbolic states according to a chaotic map using a shift register to approximate the Bernoulli shift map acting as a convolution code with a number of states equal to the symbolic states defined on the chaotic map. The pseudo-chaotically coded data is converted to analog form and modulated into synchronization frames in a transmitted signal.
The Maggio prior art has limitations in that it uses only one chaos map (e.g., Bernoulli shift map), that is generated based on the data transmitted. By confining the mapping to Bernoulli shift, information that is repeated in each transmission or repeat symbol can be recognized after observing the waveform over an extended period of time. Once compromised, all future data will be detectable and decodable by a hostile system.
Another prior art system that teaches a chaotic coding/modulation method is described in U.S. application Ser. No. 13/190,478 (“the '478 Application”), which is commonly invented by the present inventor, and incorporated herein by reference in its entirety. The system of the '478 Application teaches a system, device and method for wirelessly transmitting data via a digital chaos spreading sequences. The '478 Application system teaches constructing and storing a digital chaos spread code sequence in a volatile memory in both the transmitter and the receiver. Information corresponding to the chaos spread sequence used to transmit the digital information is received by receiver for identifying which chaos spread code sequence to use to retrieve the coded information. The '478 Application system further eliminates the reliance on the Bernoulli shift map, and therefore teaches a system which is less detectable by a hostile system.
While the system of the '478 Application solves many of the problems in the prior art, the system may only be applied to SISO systems. The receiver disclosed in the '478 Application detects and processes only one data stream for a single user even in the presence of other users or external interference. The '478 Application therefore would not be useful for transmission systems that jointly processes a plurality of signals detected at the receiver.
Generally, the most fundamental issue in wireless communication is to determine ways to improve how efficiently and reliably data can be transmitted through a channel. Next generation multimedia mobile communication systems require a high speed communication system capable of processing and transmitting various forms of information such as images and wireless data, different than an initial communication system providing a voice-based service.
Then according to the prior art, what is needed is a system and method that does not sacrifice data rate in favor of range, provides increased robustness, while improving LPI/LPD. A system and method is further needed that does exhibits the same positive improvements in a system detecting and receiving multiple signals.
Cooperation amongst multiple wireless nodes is often required in mobile ad-hoc networks (MANETs) to facilitate communication between wireless mobile nodes that are allowed to move randomly within a packet radio network. The nodes of the MANET network must find a way to communicate without knowledge of the network topology, which is the foundation for requiring cooperation among the nodes. The nodes of the network must learn the transmit and receive schedules of neighboring nodes to communicate. The communications between nodes is complicated by the mobile nature of the nodes. Discovery of neighboring nodes' schedules entails organizing the nodes into individual group formations, assigning the nodes a group membership assignment, and broadcasting the group's messaging capability to disseminate the essential health of the group to members and, potentially, disseminate the health of any non-members in certain circumstance. The rate of resolving the scheduling must be fast and bandwidth efficient such that the network can be stabilized yet updated often enough such that the information collected has not become stale. Therefore, the lightness in overhead and relative speed of generating the channel schedules become important factors in the design of the Media Access Control (MAC) layer in cooperative network. A number of the unique characteristics of digital chaos signal structure simplifies these operations compared to prior art. In particular, the property that several digital chaos signals can exist on the medium simultaneously without causing a collision greatly reduces the time need to disseminate group health or status information to all members of the group and hence changes the method of discovery for the schedule of neighboring nodes. Another property that helps reduce the number of exchanges in handshaking between nodes is that a unique broadcast digital chaos signature derived from a device's unique identifier, such as unique 15-digit IMEI or ‘International Mobile Equipment Identity’ number, is preload in the devices non-volatile memory. Since the IMEI is unique for each cellular device, the association and authenticate process can be performed simpler and more secure than the prior art for similar process steps in other radio protocols. Last, the orthonormal property of the digital chaos signals allow channel sensing to be perform on a per user basis as well as the total users occupying the media at the time.